The six women vying for the Democratic Party’s presidential nomination in 2020 start the race with more than 1 in 10 Americans saying they’re less suited to politics, merely because of their gender.

A new report from Georgetown University’s Center on Education and the Workforce contends the candidates — who include four senators, Kirsten Gillibrand of New York, Kamala Harris of California, Amy Klobuchar of Minnesota and Elizabeth Warren of Massachusetts, along with Hawaii Rep. Tulsi Gabbard and author Marianne Williamson — face a deficit that’s “still too substantial to ignore.”

Authors Anthony P. Carnevale, Nicole Smith and Kathryn Peltier Campbell base it on the General Social Survey, an annual study begun in 1972 and conducted by the National Opinion Research Center at the University of Chicago, which found last year that 13 percent of Americans are still biased against women in politics, down from a peak of almost 50 percent in 1975.

But a deeper look at the campaigns of actual women candidates, based on studies across decades, calls their pessimism into question. Robert Darcy and Sarah Slavin Schramm of George Washington University wrote in a 1977 article that a congressional candidate’s gender had “little or no effect on election outcomes,” for example.

In 1985, John Zipp and Eric Plutzer of Washington University in St. Louis found the same in their study of 1982 Senate and gubernatorial races. In 1994, Barbara Burrell of Northern Illinois University wrote in her book, “A Woman’s Place Is in the House: Campaigning for Congress in the Feminist Era,” that women are as successful at winning elections as men.

More recently, Kathleen Dolan of the University of Wisconsin in Milwaukee found that women running for the House in 2010 won at rates as good as or better than the men. She detailed her research in the 2014 book “When Does Gender Matter? Women Candidates and Gender Stereotypes in American Elections.”

It’s not that some Americans aren’t sexist, Dolan argued, but that their party loyalties overwhelm their preconceived notions. Republicans will vote for a woman Republican over a Democratic man, even if they think men are generally better suited for governing.

Also watch: Elizabeth Warren is running for president — Here are some congressional basics

The reason women remain so underrepresented in political office is not because they face discrimination at the ballot box, but because so few run, which may well be the result of underlying sexism.

Dolan and many others have found that men are much more likely than women to view themselves as strong candidates for elective office. So women tend to wait until they have more political experience. The women Dolan studied in 2010 were significantly more likely than the men to have served previously in a state-level office.

Sexism may be contributing to the skepticism facing the six women running for president, for fear they could meet the same fate as Hillary Clinton in 2016. Still, if Clinton was the victim of bias, she nonetheless won the votes of nearly 3 million more Americans than Donald Trump did and, if not for America’s electoral system, would be president.